Combustion control



April 27, 1943. F. H. LoF-rus I GOMBUSTIYONCONTROL Filed Nov. 19, 1941am u INVENTOR JM/ 025 Patented Apr. 27, 1943 UNITED STATES PATENT OFFICECOMBUSTION CONTROL Fred H. Loftus, Pittsburgh, Pa.

Application November 19, 1941, Serial No. 419,713

3 Claims.

The invention relates to industrial furnaces, such as the metallurgicalfurnaces used in the smelting and refining of metals, glass, and thelike, and furnaces used in the heating and annealing of articles formedof metal, glass, or other material.

More particularly, the invention relates to the combustion of fuel thatis required in the operation of such furnaces. The invention consists inimprovements in method.

In the operation of an industrial furnace, the rate at which theflame-sustaining fuel and air are projected into the furnace chamber isessentially subject to control, in order that the rate of heatgeneration within the furnace may be regulated, and in many cases it isdesirable that the flames within the furnace shall be held to definitepaths or trajectories, thisbeing particularly true in the case of theopen-hearth furnaces of the steel industry.

I shall describe the invention as it is practised in the operation of agas-fired open-hearth furnace, with the understanding that thedescription is exemplary of the many other fields in which the inventionwill find utility.

The usual open-hearth furnace is fired through a port at one end of thefurnace, and the prod-- nets of combustion escape through a port at theopposite end. From time to time the operation is reversed, and the portwhich had been serving as the firing port becomes the outgo port, andthe port which had been serving as the outgo port becomes the firingport. A already mentioned, it is desirable that (in the intervalsbetween such reversals) the flame projected from the firing port shallbe held to a predetermined trajectory, the object being to hold theflame, hot gases, and heat in the region of the furnac chamber in whichthey will operate with greatest effect upon the furnace charge, and withminimum deleterious effect upon the refractory roof and walls of thefurnace structure. While it is possible so to design a furnace that, fora given fuel and a given temperature of furnace operation, the flamewill have the desired trajectory, the conditions of service havehitherto prevented the full realization of such desideratum.Specifically, the temperature within the furnace must be modified as thesteel-refining operation progresses, and for this reason the quantity offuel delivered into the furnace must be varied, with the consequencethat the volume and velocity of the combustible m'"- ture projected intothe furnace are altered, whereby the flame follows a different path thanthat desired.

With these circumstances in mind, it"is to be understood that myinvention consists in an improved method of holding the flame to thdesired trajectory, while varying the heat-producing effect of theflame. In accordance with the invention, an adulterant is mixed with thestream of fuel gas'which flows under pressure into the firing port ofthe furnace, and such adulterant consists in fluid fuel of different B.t. u. value than said fuel gas, or in some cases it may consist partlyor entirely of a non-combustible fluid. The quantity of the fuel, whichcomprises one of the ingredients of the mixture, is adjusted accordingas the temperature -requirements of the furnace vary, while the quantityof the adulterant (the adulterant comprising the other ingredient of themixture) is regulated under the effect or influence of the pressure ofthe mixture in such manner that the velocity of the mixture is held tosubstantially constant value. Thus, the B. t. u. content of the mixtureis modified as need be, and the flame held to the predetermined optimumtrajectory.

In the accompanying drawing, Fig. I illustrates an open-hearth furnacediagrammatically in side elevation, and in association with the furnaceapparatus for the practice of the invention is shown schematically. Fig.II is a fragmentary view of the apparatus, illustrating a modification.

Referring to the drawing the open-hearth furnace I is provided at itsends with conventional ports 2 and 3. The ports communicate throughregenerator chambers 4 and 5 and flues 6 and 1, respectively, with anair inlet 8 and a stack duct 9. Fuel pipes m and II extend from a fuelsupply pipe IE to the furnace ports severally, and the usual reversingvalves l3 and M are arranged in the flue and fuel-delivering systems, asshown.

In the customary operation of the furnace, the port at one end of thefurnace (the port 3, as here shown) serves as the firing port, while theport at the opposite end of the furnace (the port 2) serves as the outgoport. The valves 13 and M are so adjusted that fuel (in this casenatural gas or coke-oven gas) flows from supply pipe [2 and.

through pipe H to the port 3, while air enters flue I from inlet 8, andstreams upward through the hot checkerwork of regenerator 5 into theport. The fuel and air intermingle in the port and provide acombustion-sustaining mixture that in known way streams into the furnacechamber that bears on its hearth a bath B of molten steel undergoingrefinement. And with the valves I3 and I4 so adjusted, communicationbetween the pipe ll] of port 2 and the fuel supply pipe |2 is blanked,and there is open communication between the flue 6 and the duct 9. 'I'heduct 9 opens into a stack (not shown). The hot products of combustion,escaping through port 2 from the metal-refining chamber of the furnace,are under the effect of the stack drawn downward through the regenerator4, and ar caused to yield large stores of heat to the checkerworkthereof, and from the bottom of. such regeneratorthe waste products flowthrough flue 6 and duct 9 to the stack. Thus a burning column of fueland air sweeps into the furnace from one end, and the products ofcombustion escape from the opposite end. From time to time the valves l3and I4- are swung into alternate positions, and operation of the furnaceis reversed; the port 3 becomes the outgo port and the port 2 the firingport. The heat yielded to the checkerwork of regenerator 4, while port 2was serving as outgo port, is now yielded to the air streaming upwardthrough the regenerator into port 2. Such in general is the usual.operation of'an open-hearth furnace.

As mentioned in the introduction to this specification, it is desirablethat in the intervals between the successive reversals of the furnacethe flame delivered by the firing port upon and across the charge orbath on the furnace hearth shall be held to a predetermined path ortrajectory, While the temperature within the furnace is regulated asneed be. In the drawing the broken-line arrow T indicates the desiredflame trajectory when. the port 3 serves as the firing port, and it willbe understood that when the port 2 becomes the firing port the desiredflame trajectory will be opposite in direction but in other respects thesame as the trajectory indicated.

In the preferred practice of the invention an auxiliary supply of fuelis provided, and the auxiliary fuel comprises an adulterant having lowerB. t. u. value than the principal fuel delivered by the pipe l2. Whenpeak temperature is desired in the furnace all of the fuel delivered tothe firing port may be the high B. t. u. fuel from the pipe l2, -butwhen some lower temperature is desired in the furnace I introduce inregulated quantity the auxiliary fuel or adulterant into the combustiblemixture of air and fuel supplied to the firing port, and in consequenceI modify the heat-generating capacity of the flame that is sustained inthe furnace chamber. The quantity of the principal fuel relatively tothe quantity of the adulterant is nicely regulated, so that the heatgenerated by the flaming mixture projected into the furnace will beadequate to afford the temperature desired. While thus controlling theheat-producing capacity of the combustion-sustaining stream, I maintainthe velocity and quantity of the mixture streaming from the firing portsubstantially constant, with the effect that the flame is held to thepredetermined ptimum trajectory. Thus, I maintain a constant flametrajectory, while varying the temperature conditions within the furnace.

Various apparatus may be used in the practice of the invention, and theshowing in the drawing hereof is exemplary only.

I provide an auxiliary fuel inlet I5 that in this case opens into themain fuel pipe l2 on theupstream side of valv l4. Whereas the fuel(typically natural gas or coke-oven gas) supplied by pipe I2 is of highB. t. u. value, the adulterant supplied by the pipe I5 is of relativelylow B. t. u. value, say blast-furnace gas. In the extent of pipe l5provide a gas washer I6, a pressureboosting fan or turbine I1, anautomatic pressure regulator l8, and a check valve IS. The pressure ofthe mixed fuel and adulterant is the elfective agency that controls theregulator l8, a branch pipe 20 providing the essential communication. Inthe main fuel pipe I2 I provide a control valve 2|, a meter 22 and anautomatic pressure regulator 23, arranged in the order named on theupstream side of the delivery end of auxiliary fuel pipe |5 The valve 2|is manipulated to vary the quantity of fuel delivered by pipe i2 inaccordance with the temperature requirements of the furnace, and suchvariation in the quantity of fuel delivered produces a variation in thepressure of the mixture of fuel and adulterant. The regulator I8responds immediately to such variation in the pressure of the mixture,and makes a compensating adjustment in th flow of adulterant from pipel5, whereby the pressure of the mixture is immediately restored tooriginal value. Thus, when the opening of valve 2| is decreased thequantity of adulterant flowing from auxiliary pipe I5 is automaticallyincreased, and the heataffording capacity of the flame within thefurnace is reduced. Alternately, when the opening of the valve 2| isincreased, the quantity of adulterant admitted'to pipe l2 drops, and incase such valve is turned into fully opened position, to obtain a peaktemperature in the furnace, the flow of fuel from pipe IE will beentirely arrested, and. the check valve I9 will close. In any event thevelocity of the mixture is maintained at substantially constant value,while the B. t. u. content of the mixture is modifiedi in accordancewith the temperature requirements of the furnace. It will be understoodthat, with the velocity of the combustion-sustaining air maintained inthe usual way at substantially constant value, the above-describedregulation of the. mixture is effective-to control the Velocity of theflame-sustaining column sweeping from the firing port into the furnace.

While I have specified blast furnace gas as the auxiliary fuel I use, itis to beunderstood that other fuels or gases may provide the auxiliaryfuel or adulterant. As an example I may draw flue gas from the stackflue of the open-hearth furnace' being fired, and in Fig. II of thedrawing such expedient is diagrammatically indicated. The pipe 24 isarranged to deliver flue gas from the stack duct 9, through the washerl5, pressure booster |1, and the regulator It, to the main fuel pipe I2.

I claim as my invention:

1. In the operation of a furnace in which a flame-sustaining stream offuel having an adulterant mixed therewith is projected into the furnacechamber, the method of regulating the heat of the flame while holdingthe flame to a substantially constant trajectory which comprisesregulating the fuel in the stream to alter the heat-producing valuethereof, and under the influence of the pressure of said streamautomatically regulating the adulterant in the stream to hold thevelocity of the stream substantially constant.

2. In the operation of a furnace in which a flame-sustaining streamincluding a mixtur of two fuels of different B, t. u. contents isprojected under pressure into the furnace chamber, the method ofregulating. the heat of the flame while holding the flame to asubstantially constant trajectory which comprises regulating thequantity of one of the fuels in the stream to alter the heat-producingvalue thereof, and under th influence of the pressure of said streamautomatically regulating the quantity of the other of said fuels in thestream to make compensation for the regulation of the first fuel andhold the velocity of the stream substantially constant.

3. The method of regulating th heat of a flame projected into a furnacewhile holding the flame to a substantially constant trajectory by thein- FRED H. LOF'I'US.

